Nitrogen fertilisers used to increase crop yields in China are having ‘extreme’ environmental consequences, according to a study from leading soil scientists.
Scientists from China, the UK and the United States measured the pH of soil samples taken from agricultural land across China in the 1980s and 2000s and found widespread acidification caused by nitrogen fertilisers.
On average, the pH of soil across the country had decreased by 0.5 in 20 years. In parts of Hunan province, in south China, the pH of the soil had dropped to between 3 and 4.
Most crops are suited to a neutral range between pH 6 and pH 8.
Intensification drive
Dr Goulding, head of soil science at Rothamsted Agricultural Research Centre, said Chinese farmers had been encouraged to use more fertilisers to drive up yields, but had not been warned about the risks.
‘The message from the Chinese government was very simple: put nitrogen fertiliser on your crops and get more yield. The result in many parts of the country is extreme acidification,’ said Goulding.
Professor Peter Vitousek of Stanford University, who worked on the study, said the amount of fertiliser being used in China was ‘mind-blowing.’
‘Whereas on a grain farm in Illinois, an average of 200 kg of nitrogen fertiliser are being used per hectare, on a maize farm in China that could be as much as 800 kg per hectare.
‘More than half of that is not going into the crop: instead it's having grave environmental consequences downwind and downstream,’ he said.
Cutting fertiliser usage
Professor Vitousek said the research had shown that farmers could cut the amount of nitrogen fertilisers used almost in half without affecting yields.
'This would be an absolute benefit to the environment and farmer costs,’ he said.
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